That was my thought too. A 3 sniper team. One decides to just leave (because he is the real shooter or to help the real shooter?), then another one leaves (to help the first sniper who left and/or assist the real shooter), leaving only one left. The last guy standing could have been the real shooter too or a spotter, making sure the real shooter was undisturbed or to raise alarm if needed.The 'police snipers' in the building behind Crooks are now my top suspects. As accomplices, if not actual assassins.
It would be interesting to know who those 3 guys were in the 'police' sniper team and their backgrounds/previous experiences etc.
A question for the C's would be how many people were involved/informed in this assassination attempt (from planning, execution to clean up and muddling of the waters). It could well be in the hundreds, though many of which would be on a hierarchical need to know basis.